An update to my earlier post:
rMBP Late 2013 - 16GB Ram, i7, NVIDIA GeForce GT 750M 2048 MB
OS X 10.9.2
Connected to Thunderbolt display running at 2560 x 1440
rMBP screen not in use.
I’m not sure if this helps, I was running the spotify plugin, and I enabled the “Show Equalizer” option (although it’s just a looped animation) once I disabled it and restarted atom the cpu went back down to around 5/6% again.
Today however the entire app itself is feeling very slow, 3/4 tabs open, one window and it’s very sluggish copy and pasting small chunks of text. Typing is slow etc. Can’t pin point what cause it. Its seems to slow down the longer I use the app, it is the way it handles history/steps?